The present invention relates to an electronic governor for internal combustion engines, and more particularly to an electronic governor for electronically controlling the adjustment of the amount of fuel injected by a fuel injection pump for an internal combustion engine.
In general, governor speed characteristics for internal combustion engines are classified into two types: the all-speed governor characteristic in which the governing operation is carried out for the entire speed range from idling speed to maximum engine speed and the minimum-maximum governor speed characteristic in which the governing operation is carried out for the maximum speed state and the idling speed state of the engine and no governing operation is effected in the medium engine speed range therebetween. The former characteristic is suitable for the case where the engine should be operated at a specific constant speed, as in the case of electric generators, hydraulic equipment, machines for construction and civil engineering work, and the like (called simply "machines" hereinafter), and the latter characteristic is suitable for a vehicle whose speed is controlled in accordance with the operation of an accelerator pedal depending upon the load or road condition.
Therefore, in the case where a single internal combustion engine is used both for driving the vehicle and for operating a machine, as in the case of a vehicle equipped with a machine, it is desirable to provide an arrangement for switching over the governor characteristic.
In the prior art, an apparatus capable of switching over the governor characteristic is disclosed in Japanese Patent Application Disclosure No. Sho 56-148635. The disclosed electronic governor has a control signal pattern generator for the all-speed range and another control signal pattern generator only for high speed and low speed and the output of one or the other of these two control signal pattern generators is selectively derived by the operation of a snap switch.
However, since the disclosed apparatus is constituted in such a manner that the switch for changing the governor characteristic has to be operated by the operator, there is a danger that the governor characteristic may be changed to the other state by a misoperation while the engine is being controlled in the desired state. If this should happen, the engine speed will suddenly change, which may damage the equipment being operated (vehicle or machine) and in many cases will expose the operator to considerable danger. Furthermore, it is sometimes impossible to apply the disclosed apparatus to an existing piece of equipment for the lack of space on the control panel for the required switch.